1. Field of the Invention
The present invention relates to a semiconductor device including a schottky barrier diode and a method of manufacturing the semiconductor device.
2. Description of the Related Art
Conventionally, an inverter circuit is used for driving an alternate current diode with a high efficiency, for example. An inverter circuit 80 according to an example of the related art includes switching elements 81 and freewheeling diodes 82, as shown in FIG. 19. The switching elements 81 and the freewheeling diodes 82 are coupled in parallel for driving a motor (not shown) at three phases including a U-phase, a V-phase, and a W-phase.
For example, a low-loss insulated gate bipolar transistor (IGBT) may be used as the switching element 81, and a fast recovery diode (FRD) having a high reverse-recovering property may be used as the freewheeling diode 82. When the freewheeling diode 82 as the FRD is operated in a forward direction, a lifetime of a minority carrier is controlled to be short. While having a merit that reverse-recovering time is short, the freewheeling diode 82 has a demerit that a forward voltage VF becomes high and a flowing-back loss becomes large.
A schottky barrier diode (SBD) has a low forward voltage VF and a high reverse-recovering property. However, the SBD that has a silicon (Si) simple structure is difficult to resist an electric voltage over 200 V. Thus, a super junction SBD (SJ-SBD), in which a super junction structure and the SBD are combined, is used. In the SJ-SBD, the SJ structure has a PN diode, and the PN diode and the SBD are arranged in parallel. Thus, an electric current flowing to the PN diode is restricted for showing the high reverse-recovering property.
JP-2000-349304A and JP-2002-76370A respectively disclose a schottky barrier diode in which a positive (P) column that configurates the SJ structure is provided as a floating region. When a reverse bias is applied to the PN diode, the P column functions as a source of the minority carrier, and thereby the reverse-recovering property of the SJ-SBD is improved.
However, the floating state of the P column has a possibility of causing a variation in performance and a deterioration of a reliability of the freewheeling diode. A performance required for the freewheeling diode is shown in FIGS. 20A-20C. Regarding to a reverse property shown in FIG. 20A, it is preferred that a leak electric current IR is low and a voltage resistance VR is high. Regarding to a forward property shown in FIG. 20B, it is preferred that a forward voltage VF is low. Regarding to a reverse-recovering property shown in FIG. 20C, it is preferred that a reverse-recovering time Trr is short and a reverse electric current IR is low.
However, when a forward voltage VF of the PN diode is low, a through current and a reverse-recovering property are reduced. Thus, the forward voltage VF and the reverse-recovering property have a trade-off relation and it is difficult to ensure compatibility between the forward voltage VF and the reverse-recovering property.
In addition, when the SBD is configured to have a high voltage resistance, the forward voltage VF is required to be high and a flowing-back loss is difficult to be reduced. Thus, the forward voltage VF and the voltage resistance of the diode have a trade-off relation and it is difficult to ensure compatibility between the forward voltage VF and the voltage resistance.
Therefore, it is difficult to ensure all of reducing the forward voltage VF, increasing the voltage resistance, and improving the reverse-recovering property.